The invention relates to a flow control valve for preventing gastric distention and aspiration of stomach contents due to excessive gas flow rates delivered to patients by controlling the flow rate of pressurized air from a manually operated resuscitation device, such as a Bag-Valve-Mask device, pocket mask, face shield, or endotracheal tube.
In the relevant art of pulmonary resuscitation using manually operated resuscitation devices, the Bag-Valve-Mask resuscitator (commonly referred to as a xe2x80x9cBMVxe2x80x9d) has been the primary method of ventilating the patient in respiratory arrest for some 40 years. The BVM device is well known to those in the relevant art and examples of BVM designs are shown in U.S. Pat. Nos. 4,532,923 and 4,622,964 to Flynn. Cardio-pulmonary resuscitation (CPR) can be administered mouth-to-mouth without protection but recently to protect the patient and emergency medical personnel, use of various protective manually operated devices is common. For example, one way valves, patient exhalation valves and fabric shields are fitted to pocket masks and face shields in order to inhibit cross-contamination.
The clinical application of manually operated resuscitation devices including BVM devices, pocket masks, and face shields however is not based on scientific fact but rather on historical usage and the lack of an inexpensive alternative. Potentially dangerous excessive gas flow rates and pressure delivered to the patient have been documented using mechanical BVM""s as well as the exhaled breath from the operator using pocket masks and face shields. The skill and training of the operator alone determines the efficacy of resuscitation when manually operated devices are used.
Clinical evidence that supports the use of BVMs is rare, whereas there is an abundance of evidence that clearly identifies BVMs as generally ineffective in providing adequate ventilations to the patient [for example, A. H. A. Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiac Carexe2x80x94J. A. M. A. Oct. 28, 1992:2171-2295].
The BVM consists of a self inflating balloon at one end having a one way intake valve that allows gas to be drawn into the balloon as the balloon recoils after it has been manually squeezed by the user. The intake valve self seals when the inflated bag is squeezed, and opens when the bag is permitted to recoil naturally. On the other end of the balloon, a one way output valve permits the gas to leave the bag when squeezed directing the flow of gas to the patient through a facemask, or other airway adjunct. The output valve opens when the inflated bag is squeezed, and self seals when the bag is permitted to recoil naturally. The output valve when sealed diverts the exhausted gas from the patient out through an expiratory port on the valve housing. As a result of cyclical manual squeezing and recoil of the balloon, gas is pumped through the balloon to the patient mask.
The original BVM was a development from the xe2x80x9cBlack Anaesthesia Bagxe2x80x9d whereby the black bag was supported internally by a foam, self inflating balloon causing the bag to recoil to its original shape when the squeezed bag was permitted to recoil when released.
Many versions of the BVM have been developed all with the same negative feature, namely that the delivered flow, tidal volume, airway pressure and frequency are totally dependent upon the operator""s skill and hand size. The inability to control the output from the BVM has been subject of many studies and has been well documented. Prior to creation of the present invention, this problem has not been overcome. [For example: Cummins R. O. et al, Ventilation Skills of Emergency Medical Technicians: A Teaching Challenge for Emergency Medicine, Ann. Emerg. Med, October 1986; 15:1187-1192; Stone B. J. et al, The Incidence of Regurgitation During Cardiopulmonary Resuscitation: A Comparison Between the Bag Valve Mask and Laryngeal Mask Airway, Resuscitation 38 (1998) 3-6; Elling, B. A. et al, An Evaluation of Emergency Medical Technician""s Ability to Use Manual Ventilation Devices, Ann. Emerg. Med. 12:765-768, December 1983; Rhee, K. J. et al, Field Airway Management of the Trauma Patient, The Efficacy of Bag Mask Ventilation, Am. J. Emerg. Med. 1988;6:333-336; Manoranian, C. S. et al, Bag-Valve-Mask Ventilation; Two Rescuers Are Better Than One: Preliminary Report, Critical Care Medicine, 1985;13:122-123; Lande, S. et al, Comparing Ventilatory Techniques During CPR, J. E. M. S. May 1982; Harrison, R. R. et al, Mouth-to-Mouth Ventilaion: A Superior Method of Rescue Breathing, Ann. Emerg. Med., 11:74-76, February 1982].
Additionally, the requirements of ventilation have changed in recent years causing more concern over the use of the BVM and the volume, frequency of ventilation, airway pressures and flows that the average skilled operator can deliver. A number of the above clinical papers have documented this inability by even highly skilled operators to consistently deliver correct volumes and ventilation rates without causing problems for the patient including gastric distention and aspiration of stomach contents leading to patient morbidity and even death. Not only BVM""s result in unsatisfactory ventilation but any manually operated resuscitation device including pocket masks and face shield yields similar results due to the reliance on the skill and training of the operator.
The quality of ventilation delivery when operator powered devices are used is particularly unpredictable and varies greatly according to experience, training and general coordination ability. To provide adequate ventilation, the emergency medical technician should pay attention to consistently timed tidal volumes of approximately equal volume and pressure dependant on the body size and age of the patient. However emergency care personnel are often under extreme stress and have many other duties to perform in urgent care situations that tend to reduce the attention and level of care directed to ventilation techniques.
While normal breathing requires muscle action (diaphragm, intercostals and others) to produce a negative pressure (subatmospheric or vacuum) within the chest to draw air into the lungs, artificial ventilation is accomplished by forcing air or oxygen into the lungs under an external positive pressure.
The positive pressure required to deliver a set volume (tidal volume) of gas to a patient is dependent on two factors: (1) the compliance, stiffness or elasticity of the lung, and (2) the resistance to gas flow within the conducting airways. For example, a xe2x80x9cstiffxe2x80x9d lung that is damaged by pulmonary fibrosis, disease or trauma requires a higher pressure to deliver a set tidal volume than a normal elastic lung. Similarly, gas will encounter less resistance through a normal airway that is not narrowed by bronchospasm or asthma, kinked by a poor airway opening technique, or plugged with blood, mucous, vomit or other debris.
As a result, manual and automatic ventilation techniques must accommodate a range of pressures. With a cormnon tidal volume of gas that is delivered, the patient""s lung and airway condition will determine the pressure needed to ventilate the patient. However, there is a safe upper limit to the pressures that can be used to prevent lung damage. The danger of pneumothorax or lung rupture due to excessive pressures is considered to occur between 75 and 85 cmH2O.
Regarding the peak flow rates required to adequately ventilate an adult in respiratory arrest a generally accepted rate is a tidal volume of one liter at 12 breath cycles per minute. The breathing rate of 12 breath cycles/minute equals 5 seconds/breath cycle (60/12). Assuming that it takes about one half the length of time to inhale as to exhale (1:2 IE Ratio), the inhale portion of the breathing cycle takes approximately 1.5 seconds/inhaled breath (5 seconds/3=1.67 or approx. 1.5). The ideal flow rate therefore is approximately 40 liters/minute derived by (1 liter per inhaled breath/1.5 seconds per inhaled breath)xc3x9760 seconds per minute=40 liters per minute.
Therefore the accepted limit of ideal flow rate is in the order of 40 liters per minute and limit of maximum pressure is approximately 75 and 85 cmRH2O. Tests conducted however indicate that excessive peak flows of 200 liters/minute at pressures of 100 cmH2O are commonly delivered when fully trained emergency medical personnel use the manual ventilating techniques involving Bag-Valve-Masks and mouth-to-mouth resuscitation, with patient isolating valves on pocket masks and face shields.
The problem in the emergency medical service field is that users generally perceive that they are competent in using the manual devices and that the manual devices and methods themselves are efficacious. Many technicians claim that the manual xe2x80x9cfeelxe2x80x9d of the BVM allows them to make clinical judgements on the patient""s lung condition. In reality what they are feeling is the backpressure created by the high flow rates generated when squeezing the bag too hard or for too short an inspiratory time. The backpressure condition masks the actual compliance and resistance of the patient""s airway.
Judging from the clinical research, noted above, these beliefs are totally unfounded. Ideally, an automatic ventilator with appropriate patient condition monitoring circuits and cautionary alarms can be used to provide consistent care to the patient. However, due to the perceived high cost, many decision-makers are not persuaded to spend the extra funds on automatic devices since they perceive that the manually operated devices function efficiently. Such short term thinking does not consider the true cost of disposable BVMs, pocket masks and face shields including the risk to a patient""s health by depending entirely on the skill and attention of an operator.
The prior art has proposed solutions that do not control the gas flow, but provide high pressure relief exhaust ports or an indication of the gas pressure within a BVM circuit. The prior art does not appear to recognize that excessive pressure and flow rates can be delivered from pocket masks and face shields as well.
For example, U.S. Pat. No. 5,557,049 to Ratner discloses a disposable manometer, which is used on a BVM device to indicate the pressure of gas being delivered to the patient. The Ratner solution presumes that the user has time and attention available to view the manometer and adjust their ventilation efforts accordingly. However, in reality during literally life and death situations the operators are constantly preoccupied. The bag-valve-mask requires almost continuous contact with one hand of the user and thereby imposes extreme limitations on their actions. In an effort to accomplish more than one task at a time, the operator can easily neglect the bag-valve-mask or deliver inconsistent ventilation to the patient.
U.S. Pat. No. 5,722,394 to Loescher shows an example of a BVM including a high pressure exhaust valve. U.S. Pat. No. 5,537,998 to Bauman provides a spring loaded piston which serves to detect and exhaust excess air pressure in a simple manual resuscitator with vent ports open depending on the extent of internal pressure delivered to the patient with the manual resuscitator.
None of the prior art devices specifically prevent stomach aspiration and distention by controlling the flow rate, pressure or volume of gas with any degree of accuracy.
It is an object of the present invention to control the flow of gas during respiratory resuscitation thereby limiting the gas flow between a minimum and maximum being manually delivered by the operator.
It is a further object of the invention to provide control of gas flow by modifying the established disposable BVM, pocket mask or face shield to ensure acceptance with minimal increase in price.
Further objects of the invention will be apparent from review of the disclosure and description of the invention below.
The invention relates to an improved bag-valve-mask (BVM) device with flow control valve to eliminate the danger of patient distension and aspiration of stomach contents during ventilation. The BVM having the usual patient mask with a gas inlet and flexible patient face sealing edge, flexible manually squeezed bag with a one way intake and output valves in flow communication with a gas source and the mask inlet, and exhaust port for exhausting exhaled gas from the mask when the bag output valve is closed. The flow control valve is interposed between the mask and bag to automatically and variably limit the rate of gas flow from the bag to the mask between a predetermined minimum flow rate and a maximum flow rate.
Further details of the invention and its advantages will be apparent from the detailed description and drawings included below.